Hi Maria, I think in Spain we would say something like this :"Hasta llegar a las baterías, la corriente pasa por un controlador, que apaga el flujo cuando las baterías están llenas/cuando las baterías se llenan". If you want to use the word "camino" the correct expression would be "De camino a", and, as far as the word "flow" is concerned, I would use normally "corriente", but it sounds rather repetitive with the near presence of "current", so, between "flujo" and "fluido", I think the former is preferred. From my point of view, "fluido" is more used when talking about liquids. I hope you find this information useful.